Ocean radar

Summary

Radar antenna Image credit: Paul Lethaby, UWA.

Coastal currents communicate a wealth of information and properties such as heat and nutrients. In addition they provide a mechanism for larval dispersal, pollution transport, and sediment redistribution. However, until recently, spatial data was very difficult to find, as direct measurements are usually at a single point from moorings. In addition, with over 80% of Australians living within 50km of the coast, sea level rise and coastal erosion are risks which affect the majority of the population. HF ocean radars installed by the Ocean Radar Facility provide maps of ocean surface currents representative of the upper 1-2 m and in some locations significant wave height and wind direction within 200km of the coast.

HF ocean radar systems provide maps of surface currents over meso-scale areas (typically up to 150km x 150km) of coastal ocean at unprecedented temporal and spatial resolution: they can range from 5 minutes to 1 hour, and 1.5 to 5 km, respectively. Deployment of the radars is in support of research in regional IMOS Nodes where there is a range of identified questions concerned with boundary currents and associated eddies, and their interaction with the shelf water and topography. These physical phenomena are linked to productivity and connectivity of biological populations, and to management issues such as coral bleaching and disease transmission. Additionally, the ocean radar systems provide a basis for applied research into wave modelling and offer test sites for hydrodynamic modelling. The high temporal and spatial resolution in combination with the high accuracy constitutes a valid reference for improving and validating ocean circulation models.

Instrumentation and Data

Between 2007 and 2012 the Ocean Radar facility installed 12 HF radars, arranged in 6 pairs. In collaboration with the IMOS Data Management team and local caretakers at the remote sites, the Ocean Radar Facility, located now in Perth, operates maintains and processes data from these radars to provide surface current measurements which are available in real-time on the Australian Ocean Data Network (AODN) Portal. In addition to currents, wave and wind measurements are also now available on the Australian Ocean Data Network (AODN) Portal. HF Radar data can also be seen together with satellite, Argo floats, and other data on the IMOS OceanCurrent website.

The Australian Coastal Ocean Radar Network includes the two main types of ocean surface radars that are being used around the world. They are the Phased Array genre (WERA), manufactured in Germany, and the Direction Finding genre (SeaSonde), manufactured in California (US).

Application of Data

Although Australia has a long history in HF radar oceanographic research, this was quite small in scale and most Australian oceanographic scientists had not been exposed to the benefits of radar in general, or to the relative merits of the two technologies. However now interest is rising, especially in merging the radar data with models through assimilation, aimed at both improving model prediction capabilities and radar performances (Predicting circulation patterns along the south-west Australian continental shelf - Ivica Janekovic, Chari Pattiaratchi, Sarath Wijeratne, Yasha Hetzel, Simone Cosoli).

The large operational ranges of the HF radar networks (often extending offshore up to 200 km) allows for the monitoring of the major current systems along the Australian coast and the study of their spatial and temporal variability, the interaction with mesoscale eddies and the mechanisms that create these features along with the frequent smaller-scale eddies (Pattiaratchi, C.; Sub-mesoscale processes along the Rottnest continental shelf; School of Civil, Environmental and Mining Engineering/Centre for Offshore Foundation Systems seminar, 8 September 2014. Perth; Pattiaratchi, C.; Peddies and critical latitude. Australian Coastal Ocean Radar Network launch, UWA, Perth, 21 November 2014, Perth).

Additional uses include Search and Rescue activities, prawn and scallop fisheries in the Great Barrier Reef and tuna fisheries in South Australia. There is great potential in Australia, and also a big need particularly in the vulnerable Great Barrier Reef, to use HF radar for port and harbour management using both currents and wave information (Penton J & Pattiaratchi CB 2015. Surface currents on the Rottnest continental shelf, Western Australia. Proceedings of Australasian Coasts & Ports Conference, 15-18 September 2015, Auckland, New Zealand; Middleditch A., Wyatt L. and James C. 2015. Wave measurements from the Australian Coastal Ocean Radar Paper. Proceedings of Australasian Coasts & Ports Conference, 15-18 September 2015, Auckland, New Zealand).

The Ocean Radar Facility is also actively involved within the Global High Frequency Network Component of the Group on Earth Observations (GEO) [7] to support further development of HF radar networks and to promote the standardization of data products and QA/QC methodologies (Cosoli S. HF radar observations of ocean currents, waves and winds in Australia. 4th Meeting of The Global High Frequency Radar Network, Heraklion, Crete, Greece, 22-23 September 2015).